Nanocrystalline Li3VO4 dispersed within multiwalled carbon nanotubes (MWCNTs) was prepared using an ultracentrifugation (uc) process and electrochemically characterized in Li-containing electrolyte. When charged and discharged down to 0.1 V vs Li, the material reached 330 mAh g(-1) (per composite) at an average voltage of about 1.0 V vs Li, with more than 50% capacity retention at a high current density of 20 A g(-1). This current corresponds to a nearly 500C rate (7.2 s) for a porous carbon electrode normally used in electric double-layer capacitor devices (1C = 40 mA g(-1) per activated carbon). The irreversible structure transformation during the first lithiation, assimilated as an activation process, was elucidated by careful investigation of in operando X-ray diffraction and X-ray absorption fine structure measurements. The activation process switches the reaction mechanism from a slow "two-phase" to a fast "solid-solution" in a limited voltage range (2.5-0.76 V vs Li), still keeping the capacity as high as 115 mAh g(-1) (per composite). The uc-Li3VO4 composite operated in this potential range after the activation process allows fast Li(+) intercalation/deintercalation with a small voltage hysteresis, leading to higher energy efficiency. It offers a promising alternative to replace high-rate Li4Ti5O12 electrodes in hybrid supercapacitor applications.

The electrochemical reduction of CO2 at a Cu electrode was investigated in a methanol-based electrolyte using such lithium supporting salts as LiCl, LiBr, LiI, LiClO4, and CH3COOLi at low temperature (−30 °C). The main products from CO2 by the electrochemical reduction were methane, ethylene, carbon monoxide, and formic acid. A maximum faradic efficiency of methane was 71.8% in LiClO4/methanol-based electrolyte at −3.0 V versus Ag/AgCl saturated KCl. In the lithium salts/methanol-based electrolyte system, except for the case of acetate, the efficiency of hydrogen formation, being a competitive reaction against CO2 reduction, was depressed below 12%. On the basis of this work, the high efficiency electrochemical CO2-to-methane conversion method appears to be achieved. Future work to advance this technology may include the use of solar energy as the electric energy source. This research can contribute to large-scale manufacturing of useful organic products from readily available and cheap raw materials:  CO2-saturated methanol from industrial absorbers (the Rectisol process).

Carbon nanotube/nanohoneycomb diamond ͑CNT-NANO͒ composite electrodes were fabricated by introducing multiwalled carbon nanotubes into the pores of nanohoneycomb diamond of 400 nm diam using the chemical vapor deposition method. The electrochemical behavior of these electrodes was examined with cyclic voltammetry, electrochemical impedance, and galvanostatic measurements in LiClO 4 /propylene carbonate electrolyte. The behavior of Li ϩ insertion into CNTs was observed in the cathodic sweep at Ϫ3.3 V ͑vs. Ag/Ag ϩ ) in CV. AC impedance measurements have indicated that at the nanohoneycomb diamond densely deposited CNTs ͑HD CNT-NANO͒, only the Li ϩ intercalation process was observed. In contrast, the nanohoneycomb diamond modified with CNTs in low-density ͑LD CNT-NANO͒ exhibited the combination behavior of Li ϩ intercalation at CNTs and the electrochemical double-layer discharging on the diamond surface. In galvanostatic measurements, HD CNT-NANO behaved as a pure Li ϩ ion battery anode, and the specific capacity ͑per 1 g of activated material͒ was found to be 894 mAh g Ϫ1 , which is higher than that obtained for mesophase carbon materials. For LD CNT-NANO, in the initial time following the start of discharging, the behavior of the double-layer discharging was observed in addition to Li ϩ deintercalation. Suppression of the potential drops associated with Li ϩ deintercalation by rapid discharging from the electrical double-layer could increase the specific power for LD CNT-NANO. The combination function of the super capacitor and the Li ϩ -ion battery that work simultaneously supporting each other in one electrochemical cell suggests the possible realization of a hybrid electrode material with high energy density and high specific power.The boron-doped diamond electrode has emerged as an attractive electrode material due to its superior electrochemical characteristics, i.e., wide electrochemical potential window in aqueous media and low capacitance. Recently, various electrochemical application studies of the diamond electrode have progressed, including electroanalysis, 1,2 electrosynthesis, 3 and electrochemical treatment of wastewater. 4 As diamond also exhibits extreme electrochemical stability, conductive diamond can be used as a support material for electrocatalysts. This physical property is derived from the strong sp 3 bond and its extremely high density. Diamond is almost completely impervious to insertion of ions and very inert to oxidative attack. In particular Li ϩ -ion intercalation is difficult on the diamond surface, and this is a totally different property from that for carbon materials with sp 2 bonds. 5 Recently, the fabrication and electrochemical characterization of nanoporous diamond with well-ordered nanopores have been reported. [6][7][8] In nonaqueous high conductivity electrolyte ͓0.5 M-tetra-ethylammonium tetrafluoroborate (Et 4 NBF 4 )/acetonitril ͑AN͔͒, the double-layer capacitance for nanohoneycomb diamond with 60 nm diam pores was found to have a high value ͑2.1 mF cm Ϫ2 ͒, similar to th...

Li-Rich Layered Li1+x[V1/2Li1/2]O2 (x = 0-1). (2018) Chemistry of Materials, 30 (15). 4926-4934.

1. Introduction The next step in the improvement of the high-energy-density Li4Ti5O12(LTO) / activated carbon hybrid supercapacitor1 is to substitute the negative electrode (LTO) with other potential candidates with higher voltage and capacity. Here, we selected Li3VO4 (LVO) because of its low redox potential (1.0 V – 0.1 V vs. Li+/Li) and reversible insertion mechanism with high theoretical capacity (394 mAh g-1 in case of 2-electron reaction and 591 mAh g-1 in case of the 3-electron).2-4 To overcome the well-known drawbacks of LVO such as low electronic conductivity (<10-10 S m-1) and large voltage hysteresis (>500 mV) which prevent to achieve high rate performances5-7, we investigated the potentialities of a nanosized LVO (10-50 nm) hyper-dispersed within multi-walled carbon nanotube (MWCNT) matrix prepared by our original ultracentrifugation (UC) process. As expected, the rate performances are considerably enhanced for the uc-LVO/MWCNT, and in addition, the structural mechanism involved during the reversible insertion/extraction of Li is clarified thanks to a deep investigation using in operando XRD. The performances of the obtained composite show that it can be used as a LTO alternative for hybrid supercapacitors. 2. Experimental NH4VO3, citric acid, ethylene glycol and lithium hydroxide were dissolved into deionized water to form a clear orange solution. After the addition under stirring of MWCNT, the solution was subjected to the UC treatment at 80 ˚C for 5min. Then, the mixture was dried at 130˚C under vacuum for 12 h to accelerate the polymerization of ethylene glycol. A calcination stage at 300°C for 3h under air was applied to remove the polymer and a final sintering at 800˚C under N2 atmosphere allows obtaining the Li3VO4/MWCNT composite. Physicochemical characterizations were performed on the synthesized composites by XRD, XPS and TEM observation. Relation between electrochemical behavior and structure change were investigated by in operando XAFS and XRD measurements.   3. Results and discussion Successful synthesis of nanocrystalline LVO particles of ca. 10~50 nm on the surface of MWCNT was confirmed by the combination of HRTEM observation and XRD measurements. The LVO/MWCNT composite shows excellent electrochemical behavior such as high charge (delithiation) rate capability with 170 mAh g-1 per composite at a high rate of 20 A g-1, when charged and discharged down to 0.1 V vs. Li. In operando XRD patterns on the composites show the existence of irreversible structure changes acting as an activation process, where the reaction mechanism of LVO switches from a “two-phase” to a “solid-solution” reaction. The relationship between the hysteresis and Li insertion mechanism was further investigated by charge-discharge tests at different cut-off voltages. It was found that the “activated” LVO/MWCNT composites within the limited voltage window (0.76 -2.5 V vs. Li) can achieve higher reversibility and energy efficiency (low voltage hysteresis below 100mV) with ultrafast Li insertion kinetics and long-term cycle life for the needed hybrid supercapacitor applications. References 1) K. Naoi, W. Naoi, S. Aoyagi, J. Miyamoto and T. Kamino, Acc. Chem. Res., 46, 1075 (2013). 2) S. Ni, J. Zhang, J. Ma, X. Yang, L. Zhang and H. Zeng, Adv. Mater. Interfaces, 3, 1500340 (2016). 3) J. Zhang, S. Ni, J. Ma, X. Yang and L. Zhang, J. Power Sources, 301, 41 (2015). 4) Z. Liang, Y. Zhao, Y. Dong, Q. Kuang, X. Lin, X. Liu, D. Yan, J. Power Sources, 274, 345 (2015). 5) Y. Shi, J. Gao, H.-D. Abruna, H.-J. Li, H.-K. Liu, D. Wexler, J.-Z. Wang and Y. Wu, Chem. Eur. J., 20, 5608 (2014). 6) Y. Shi, J.-Z. Wang, S.-L. Chou, D. Wexler, H.-J. Li, K. Ozawa, H.-k. Liu and Y.-P. Wu, Nano lett., 13, 4715 (2013). 7) H. Li, X. Liu, T. Zhai, D. Li and H. Zhou, Adv. Energy Mater., 3, 428 (2012).